Many doors, such as household doors, are provided with a dead bolt lock in order to maintain security by bolting the door shut. The dead bolts are normally required to extend one inch into the door frame and associated latch plate. Unfortunately, the dead bolt must be released and the door opened in order to (1) pass a small object through the doorway, such as an envelope or small package, or (2) to view the persons outside the door. While a short chain may be used to prevent the door from fully opening, such a chain arrangement is often weak and provides poor security.
Other devices to secure a door or to permit partial opening of a door are disclosed in the following:
______________________________________ U.S. Pat. No. Inventor(s) ______________________________________ 1,029,693 Klein 2,407,900 Paul 3,924,885 Markovitch 3,924,886 Markovitch 3,924,887 Markovitch ______________________________________
Additional prior art, of which I am aware, is as follows:
______________________________________ U.S. Pat. No. Inventor(s) ______________________________________ 1,174,629 Slauson 1,358,885 Shimocuskies 1,896,909 Maxwell 2,062,020 Engel 2,174,890 Lipiner 2,452,151 Robins 2,772,110 Petrochko 2,784,023 Pisani 3,004,419 Falk, Jr. 4,580,820 Baber ______________________________________
An alternative to a standard dead bolt lock is a lock that can operate either in a mode similar to a dead bolt or as a latch having a Z-Bar configuration, which allows the door to open a limited distance.
Such a lock is disclosed in my earlier U.S. Pat. No. 5,244,240. In my '240 patent, which is assigned to the assignee of the present invention, the lock can alternatively: (1) lock the door in dead bolt fashion, (2) allow the door to open a limited distance, or (3) allow the door to open freely. The lock has a door-mounted latch assembly that includes a base plate, an intermediate link pivoted to the base plate, and a mode selection and latching assembly that is pivoted to the intermediate link. The latch assembly has a high strength latch member and a camming system to slide the latch member back and forth as a control knob is rotated.
A latch plate is mounted on the door frame in juxtaposition to the door-mounted latch assembly. The latch plate has a cylindrical or tubular portion with an opening for receiving the latch member. An optional sleeve fits inside the cylindrical or tubular portion of the latch plate. The sleeve has an opening for receiving the latch member. When the latch member is engaged in the tubular portion of the latch plate, the sleeve may be rotated so that the latch member is engaged in the sleeve. The latch member then cannot be directly withdrawn from the latch plate.
The embodiments disclosed in my aforesaid U.S. Pat. No. 5,244,240 are provided with means for locking and unlocking a door from the interior side of the door only. However, in every day use, it is desirable to be able to lock and unlock the lock from the exterior side of the door, such as when leaving for work in the morning or returning home in the evening.
It is also desirable to provide a system for locking the sleeve into place once it has engaged the latch member in a secured position. Such a feature decreases the likelihood that the user would disengage the sleeve from the latch member. Furthermore, such a feature provides added protection against an intruder attempting to force the door open from the exterior.
Moreover, while the alarm industry is huge, fast growing, and technically very sophisticated, the focus and concentration is on generating an alarm once the perimeter security has been breached; and no one, prior to my invention, has combined existing off-the-shelf alarm hardware and monitoring methods with a vastly improved lock that provides excellent perimeter security to prevent a breach in the first instance.